Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $149.65   12.774%   $168.7663   $168.77   $168.75   $168.80  
  Purchase #2 $46.31   4.609%   $48.4444   $48.44   $48.45   $48.40  
  Purchase #3 $134.98   6.281%   $143.4581   $143.46   $143.45   $143.50  
  Purchase #4 $213.39   12.688%   $240.4649   $240.46   $240.45   $240.50  
  Purchase #5 $9.46   3.541%   $9.795   $9.80   $9.80   $9.80  
  Purchase #6 $206.44   11.309%   $229.7863   $229.79   $229.80   $229.80  
  Purchase #7 $204.95   8.737%   $222.8565   $222.86   $222.85   $222.90  
  7 purchase totals = $965.18       $1,063.5715   $1,063.58   $1,063.55   $1,063.70